Definition

Creatinine is a metabolic product of creatine and phosphocreatine, which are found in muscle and daily production is relatively constant. A small amount creatinine is derived from meat in the diet. Creatinine is transported through the bloodstream to the kidneys. The kidneys filter out most of the creatinine and dispose it in the urine.

Creatinine clearance test measures the amount of creatinine that has been cleared from the blood and passed into the urine in a 24-hour time period.

Intended Use

The creatinine clearance test is used to estimate Glomerular Filtration Rate (GFR). GFR is a measure of how well the kidneys are working, especially the kidneys filtering units. These filtering units are called glomeruli.

Creatinine is cleared from the body entirely by the kidneys. If kidney function is abnormal, creatinine level increases in the blood because less creatinine is released through the urine.

Tests parameter performed in the laboratory

Laboratory will measure the 24 hour urine volume, creatinine level from the blood and urine and do calculation from the results.

Creatinine clearance is expressed in ml/min.

Creatinine clearance calculation

= Urine creatinine x 24hour urine volume (ml)

Serum creatinine x (24hour x 60 minutes)

Sample requirements

The test requires a 24-hour urine collection and a blood sample drawn within 24 hour of urine collection.

Patient preparation

• Avoid taking interfering medications. Medications that may increase serum/plasma creatinine and thus decrease creatinine clearance by inhibiting tubular secretion of creatinine include Cephalosporin, Aminoglycoside, Flucytosine, Cisplatin, Cimetidine and Trimethoprim.
• If possible, drugs should be stopped beforehand.
• Ensure patient drink sufficient water before start collecting and continue good hydration throughout the procedure.
• A meat free diet is recommended.

Reference range & interpretation

Reference range:

Creatinine clearance is expressed in ml/min.

Reference values are: 72-156ml/min

Reference range may vary slightly among different laboratories.

Interpretation:

Any disease or condition that affects the glomeruli can decrease the kidneys’ ability to clear creatinine and other wastes out of the blood. When this occurs, the blood creatinine level will be increased and the creatinine clearance will be decreased because not as much creatinine is able to be excreted in the urine.

A decreased creatinine clearance rate may also occur when there is decreased blood flow to the kidneys as may occur with congestive heart failure, obstruction within the kidney, or acute or chronic kidney failure.

Increased creatinine clearance rates may occasionally be seen during pregnancy, exercise, and with diets high in meat, although this test is not typically used to monitor these conditions.

Limitation of the test

24 hour urine collections may be associated with significant collection errors, largely due to improper timing and missed samples, leading to over collections and under-collections.

Clinical usefulness

Creatinine clearance test used to help detect and diagnose kidney dysfunction and/or the presence of decreased blood flow to the kidneys.

In people with known chronic kidney disease or congestive heart failure (which decreases the rate of blood flow), the creatinine clearance test may be ordered to help monitor the progress of the disease and evaluate its severity.

It may also be used to help determine if and when kidney dialysis may be necessary.

References

• Chemical Pathology Discipline, National Pathology Services, MOH, Laboratory Investigation Guidelines For Chronic Kidney Disease And Utilisation of eGFR in Adults, October 2012, Percetakan Nasional Malaysia Berhad
• http://www.nlm.nih.gov/medlineplus/ency/article/003611.htm
• https://labtestsonline.org/analytes/creatinine-clearance/tab/test
• Jacobs & Demott,Laboratory Test Handbook with Key Word Index, 5^th Edition, 159-162
• Pathology Service Handbook Hospital Kuala Lumpur, 2009, Percetakan Nasional Malaysia Berhad
• William J Marshall, Clinical Chemistry Fifth Edition, 2005, Mosby, 63-66